DESCRIPTION (adapted from the application) Sickle cell anemia and related hemoglobinopathies are among the most common genetic disorders in this country. Reactivation of fetal globin by pharmacologic agents provides therapeutic benefits in these patients by interfering with the polymerization of the mutant hemoglobin. This proposal outlines an alternative approach for augmentation of fetal hemoglobin. All vertebrate animals switch hemoglobins during development from fetal to adult type. The molecular mechanisms that mediate this process are complex. Erythroid Kruppel like factor (EKLF) is an erythroid specific transcription factor that plays a crucial role in activating beta globin expression and in consolidating the switch from fetal to adult globin. In its absence not only is adult beta globin expression abolished, but there is a competitive increase in gamma globin expression. This has led us to consider whether manipulating EKLF's molecular properties so that it acts as a transcriptional repressor might further augment and stabilize gamma globin gene expression. The above hypothesis will be tested by: (1) Constructing repressor EKLF constructs and testing them by transient transfection assays in cell lines. (2) Monitoring the functional importance of repressor constructs in differentiating embryonic stem cells and transgenic mice.(3) Analyzing the effect of repressor constructs on sickle erythropoiesis in liquid cultures. The end result of these aims will be to provide a transcriptional reagent for gene therapy approaches that will augment fetal hemoglobin levels in patients with sickle cell disease. Amelioration of the debilitating effects of this disease provides a considerable clinical rationale for pursuing this goal.